Presently, almost all private, commercial and military aircraft have Flight Data and Voice Data Recorder located at the pilot cockpit and/or at the tail section of the plane. These recorders are commonly called “Black Box”. One example of the “Black Box” is as shown in the disclosure of U.S. Pat. No. 5,890,079 entitle: Remote Aircraft Flight Recorder and Advisory System. Some of these recorders are equipped with using G Switch to automatically power the ELT in the event the plane encounters a sudden escalation of “G” force signifying a crash situation.
Modern ELT have Crash Position Indicator (CPI) using COSPAS/SARSAT and Global Positioning system to expand the ELT range capabilities.
With a coverage of 121.5 MHz, 243 MHz, and 406.025 Mhz it is now possible to locate with pin-point accuracy the last known GPS Coordinates on CPI. At present, all GPS transmission should occur above water. When an aircraft crashed in the water, the Black Box or other ELT transmissions cannot reach the satellite receiver to notify search and rescue its exact position upon crash.
The Present “Black Box” configuration for aircrafts uses a ULB system (Underwater Locator Beacon). Once activated by G Switch, ULB can operate underwater only at a maximum radius of 3,000 meters for 30 days. However in order to locate the crash position, a “Hydrophone” or alike receiving equipment must be placed in the water within the prescribed radius range. Otherwise the Black box cannot be located.